Method for the production of recombinant proteins, plasmids and modified cells

ABSTRACT

Expression plasmids comprising a nucleic acid sequence of interest controlled by a T7 bacteriophage promoter and a stabilizing region comprising all or part of the par region of the RP4 plasmid or a derivative thereof. The invention also concerns the use of said plasmids in the production of recombinant products.

This application is a 371 of International Application PCT/FR95/01178, filed Sep. 14, 1995, and which designated the United States.

The present invention relates to the production of recombinant proteins in bacteria. It relates, more specifically, to a novel method which allows an elevated production of recombinant proteins in bacteria and which makes use of an expression system which is particularly stable and efficient and which comprises a bacteriophage T7 promoter and a stabilizing region. The present invention also relates to the plasmids which can be employed in this method and to the recombinant proteins which are produced in this way.

Bacteria, in particular E. coli, can be used to produce proteins of varied origin, both from procaryotes and from eucaryotes. In particular, human proteins can be produced in E. coli. In order to do this, the structural gene, or the cDNA of the gene which encodes the protein in question, must be placed downstream of the appropriate expression signals (promoter and ribosome attachment site) which are recognized by the E. coli expression machinery. The most efficient system used in E. coli is that described by Studier (Studier et al., 1990). This system involves using a phage T7 promoter which is specifically recognized by the RNA polymerase of this same bacteriophage (E. coli does not, per se, possess any promoter which is recognized by this particular polymerase). This expression system involves induction, for example with IPTG, of the expression of the gene of the phage T7 RNA polymerase (with the latter being placed under the control of an inducible promoter such as PlacUV5 of E. coli). This induction results in expression of the gene which is placed under the control of the bacteriophage T7 promoter, which is recognized by the polymerase. Since the polymerase only recognizes the promoter which is upstream of the gene to be expressed, the latter gene is, in general, expressed at a very high level (above a few per cent of the total bacterial protein). A very large number of publications now provide instances of the use of this system which was initially described by Studier (Studier et al., 1990).

As indicated above, bacteria, in particular E. coli, are used to produce human proteins of pharmaceutical interest. If the said proteins are then to be used in various therapies, it is advisable for them to be prepared in accordance with the rules of Good Production Practice (GPP). In order to do this, it is essential to have available a production system which is reproducible and which ensures that a product is obtained which is of highly defined quality and very high purity. One of the important features of a method for producing a protein of pharmaceutical interest is the strain which is used to produce the said protein. Thus, it is necessary for this strain to be such as to ensure that the mode of production is reproducible both qualitatively and quantitatively.

At the qualitative level, for example, it is appropriate to produce a protein which is totally homogeneous, that is to say which has a primary sequence which is identical to that of the natural protein. Thus, if a point mutation, which modifies the encoded sequence of the protein to be expressed, were to be produced in a bacterial cell during the course of the fermentation, this would result in the production of a modified protein which was mixed together with the protein having the native sequence. On administration to humans, this modified protein could give rise to an immune reaction which could be very harmful to the treatment or else, in a subsequent treatment, result on this occasion in a severe immune reaction.

At the quantitative level, it is an accepted fact that a method must be reproducible. This constitutes evidence of the quality of the product which is obtained. Thus, in different production batches, the amounts of the protein in question which are synthesized per unit of biomass should be the same, for the same unit of time and using the same culture and growth conditions. A very important feature of this reproducibility of the production of the protein is the presence of the plasmid carrying the expression cassette in the bacterial cells. A fermentation method is even more under control when all the cells still harbour the plasmid at the end of the culture (before and after producing the protein). An antibiotic which selects for the presence of the plasmid is generally added to the culture medium in order to maintain the plasmid in the bacteria. This can pose a variety of problems: the cost of the antibiotic for preparing the fermentation medium; since the antibiotic cannot be sterilized by autoclaving, it is advisable to add it to the culture medium immediately prior to use; the antibiotic may not be stable and may generate transformation products which are toxic in humans or which at least lead, in certain patients, to undesirable side effects; the antibiotic may also, by itself, be toxic in humans or at least lead, in certain patients, to undesirable side effects. In the latter two cases, it will be necessary to demonstrate that the traces of toxic products, corresponding either to the antibiotic or to products derived from it, which are present in the purified product, are lower, on the basis of the doses which are to be administered, than levels which are capable of giving rise to side or toxic effects. This entails elaborate and costly studies.

The present invention solves these problems. Thus, the present invention provides a particularly efficient expression system in which there is no need for an antibiotic to be present in order to maintain the plasmid as the bacterial generations succeed each other in the fermenter. The present invention relates, in particular, to the construction of a plasmid expression system in which expression is effected by means of a bacteriophage T7 promoter and which furthermore includes a stabilizing region. The system according to the invention is particularly advantageous since, contrary to that which is observed in the case of the system of Studier et al., it enables plasmids to be maintained in all the bacterial cells after expression of the protein to be expressed has been induced and in cultural conditions in which there is no antibiotic, that is without any selection pressure. Following induction of expression, the Studier (Studier et al., 1990) plasmids are only present in a very small fraction of the cells. It is evident that the system of the invention has a powerful stabilizing effect on plasmids, thereby increasing the levels at which recombinant proteins are produced and increasing the reproducibility of the method. More specifically, the stabilizing region which is used for constructing the plasmids according to the invention is derived from the par fragment of the plasmid RP4.

The invention primarily relates to an expession plasmid which encompasses a nucleic acid sequence of interest under the control of a bacteriophage T7 promoter and a stabilizing region which comprises all or part of the par region of the plasmid RP4 or of a derivative of this region.

Preferably, the bacteriophage T7 promoter which is used in the plasmids of the present invention is the promoter for the 10 gene.

As indicated above, the stabilizing region which is used in the plasmids of the invention is derived from the par fragment of plasmid RP4 (Gerlitz et al., 1990). This fragment carries a variety of functions (in particular 5 genes designated parA, parB, parC, parD and parE) and, in particular, a protein apparently having a site-specific recombinase activity which probably enables it to resolve plasmid dimers (Eberl et al., 1994). This par fragment can be isolated from plasmid RP4 and cloned into the expression plasmids of the present invention, as described in the examples. Furthermore, this fragment can be modified prior to or following its introduction into the plasmids of the invention. Thus, the stabilizing region of the plasmids of the invention can consist of all or part of the par region of plasmid RP4 or of a derivative of this region.

In particular, the stabilizing region of the plasmids can consist of the PstI insert from the plasmid pTUG3 or of the subfragments SphI-SphI-SphI from pOH23 or SphI-SphI-ClaI from pOH41 or SphI-SphI-BamHII from pGMA28 or SphI-SphI-BamHI from pGMA27, which are described by Gerlitz et al., 1990, or of any subfragment of the PstI insert from pTUG3 which contains at least the SphI-SphI-BamHI insert from pGMA27. While the PstI insert of pTUG3 contains the parCBA-parDE genes and the flanking regions, the inserts of pGMA27 or pGMA28 only contain the parCBA-parDE' genes and the 5' flanking region. The stabilizing region can also consist of the parDE genes or of the parD gene and of its promoter region or of another promoter as has already been described by Roberts et al., 1994. This region can be obtained from the StyI-ClaI fragment which is contained in plasmid pTUG3. The stabilizing region can also consist of any combination of two, three or four par genes contained in plasmid pTUG3, for example parA-parD or parB-parD or parAC-parD or parBA-parDE either with their own promoter region or with another promoter.

The term derivative of the par region includes any fragment which is obtained by genetic and/or chemical modification of the par region and which is capable of achieving stable plasmids according to the invention. In particular, these derivatives can be obtained by means of deletions, mutations, additions, cleavages, ligations, etc. within the par region of plasmid RP4, carried out in accordance with the techniques known to the person skilled in the art. Subsequently, the functional efficiency of the derivatives can be tested as described in the examples (see Example 2, in particular).

Advantageously, the stabilizing region in the plasmids according to the present invention comprises part of the Par region of plasmid RP4. In one particular embodiment, the stabilizing region consists of the fragment contained between residues 6038 and 8499 of the sequence SEQ ID NO:1.

In a preferred embodiment, the plasmids of the invention additionally include the lacO operator and the lacI^(q) gene. Thus, it has been observed that, despite the presence of a bacteriophage T7 promoter which is specific for a polymerase which is not present in E. coli, basal expression of the nucleic acid sequence of interest takes place without inducer. This residual expression can induce some decline in the stability of the plasmid. The presence of the lacO operator and the lacI^(q) gene in the plasmids of the invention makes it possible advantageously to obtain an expression of the nucleic acid sequence which is more regulated and, in particular, to inhibit any expression in the absence of inducer. The plasmids which incorporate these elements therefore exhibit greater stability and greater control of expression. In order to achieve the desired effect, the lacO operator is advantageously located downstream of the bacteriophage T7 promoter and upstream of the nucleic acid sequence of interest, as indicated in the examples. The lacI^(q) gene is inserted into the plasmid, preferably together with its own promoter, in a region which is not essential for the desired properties of the plasmid. Thus, the gene is preferably inserted outside the par region and the expression cassette of the nucleic acid sequence of interest. The sequences of this operator and of the lacI^(q) gene are given in the SEQ ID NO:1 sequence. It is understood that, these elements can be replaced by sequences which are homologous or which possess equivalent functions.

In a particularly preferred embodiment, the plasmids according to the invention also include a transcription terminator which is situated downstream of the nucleic acid sequence of interest. Advantageously, the transcription terminator which is used is that of the bacteriophage T7 gene whose promoter is used. Preferably, the transcription terminator is the T4 terminator of bacteriophage T7.

The nucleic acid sequence of interest which is present in the plasmids according to the invention can be any sequence which encodes a protein which is of pharmaceutical or agrifood interest or which can be used for biocatalysis. The sequence can be a structural gene, a complementary DNA sequence, a synthetic or semi-synthetic sequence, etc.

Preferably, the nucleic acid sequence encodes a protein of pharmaceutical interest which is selected, for example, from among enzymes, blood products, hormones, lymphokines (interleukins, interferons, TNF, etc.), growth factors, neurotransmitters or their precursors or enzymes for synthesizing them, trophic factors: BDNF, CNTF, NGF, IGF, GMF, aFGF, bFGF, NT3, NT5, HARP/pleiotrophin, etc.; apolipoproteins: ApoAI, ApoAIV, ApoE, etc., dystrophin or a minidystrophin, CFTR protein, which is associated with cystic fibrosis, tumour supressor genes: p53, Rb, Rap1A, DCC, k-rev, etc., genes encoding factors involved in coagulation: factors VII, VIII and IX, genes which are involved in DNA repair, etc.

In a particular embodiment of the present invention, the nucleic acid sequence of interest encodes an acidic fibroblast growth factor (aFGF). The cDNA of the native form of the human aFGF gene has been identified, sequenced and cloned (Jaye et al., 1986 and 1987). This cDNA can encode different forms of aFGF depending on the presence of deletions in the N-terminal part, in particular forms encompassing 154, 140 or even 134 amino acids. Furthermore, natural or artificial variants can also be produced, these variants resulting from modifications due to deletion, mutation and/or addition of one or more pairs of bases in the native gene sequence (for example of an N-terminal methionine). In one entirely specific embodiment of the present invention, the nucleic acid sequence of interest encodes aFGF (154). The plasmid pXL2435, which exhibits the sequence SEQ ID NO:1, may be cited as a specific example.

The present invention also relates to a process for producing recombinant proteins. More specifically, the production process according to the invention consists in culturing a bacterium which contains:

a plasmid such as described above which carries a nucleic acid sequence encoding the said protein, and

the gene of the bacteriophage T7 RNA polymerase,

under conditions which allow expression of the nucleic acid sequence.

As indicated above, the interest of the system resides, in particular, in the use of a bacteriophage T7 promoter which is specifically recognized by the RNA polymerase of the same T7 bacteriophage. The bacterium which is used must therefore harbour, in addition to the plasmid according to the invention, a cassette which allows expression of the bacteriophage T7 RNA polymerase. This cassette can either be integrated into the genome of the bacterium which is employed (E. coli strain BL21, DE3), or be carried by a second plasmid or a phage, or else be present on the plasmid of the invention. Advantageously, the gene encoding the bacteriophage T7 RNA polymerase is placed, in the expression cassette, under the control of an inducible promoter such as the lac, trp or recA promoter. This then makes it possible to induce RNA polymerase production in the cell in a controlled manner and, consequently, to control expression of the nucleic acid sequence of interest, which sequence is placed under the control of the promoter which is specific for the said RNA polymerase. Preferably, the inducible promoter which controls expression of the bacteriophage T7 RNA polymerase is the E. coli PlacUV5 promoter, which is specifically induced in the presence of IPTG.

As indicated in more detail in the examples, the process of the invention thus makes it possible to produce unmodified proteins at high levels and in a reproducible manner. This process thus makes it possible to produce recombinant proteins of pharmaceutical quality on an industrial scale.

The process according to the present invention is very particularly suitable for producing recombinant fibroblast growth factors (aFGF and bFGF in particular). Thus, the present invention relates, in particular, to a process for preparing recombinant aFGF, according to which process a bacterium which harbours plasmid pXL2435 and the gene of the bacteriophage T7 RNA polymerase is cultured under conditions which permit expression of the nucleic acid sequence, and the aFGF which is produced is recovered.

The present invention will be described in more detail using the examples which follow and which must be regarded as being illustrative and not limiting.

Abbreviations employed:

aFGF: acidic fibroblast growth factor

bp: base pair

OD: optical density

E. coli: Escherichia coli

IPTG: isopropylthio-β-D-galactoside

kb: kilobases

kDa: kilodaltons

Km: kanamycin

LB: Luria-Bertani medium

PAGE-SDS: electrophoresis using a gel which contains acrylamide, N,N'-methylenebisacrylamide and sodium dodecyl sulphate.

T7: bacteriophage T7

LEGENDS TO THE FIGURES

FIGS. 1A and 1B: Construction of plasmid pXL2435.

A--Construction diagram: The AccI-NdeI fragments of 3.2 kb from pET11a and of 2.8 kb from pXL2283 were ligated to produce plasmid pXL2434; plasmid pXL2434, which had been digested with BqlII, was ligated to the 2.4 kb BamHI fragment from pXL2433 in order to create pXL2435.

B--Map of plasmid pXL2435: aFGF: gene encoding aFGF; Ampr: gene for resistance to ampicillin; Kmr: gene for resistance to kanamycin; lacI^(q) : gene which encodes an elevated synthesis of the Lac repressor; ori: ColE1 origin of replication; parDE'parCBA: genes of the RP4 par locus; pT7: T7 Φ10 promoter and lacO operator; TΦ: T7 TΦ terminator. The arrows indicate the direction in which the genes are transcribed. The restriction enzyme sites which are shown are those which were used for cloning. The numbers in brackets correspond to the positions, in base pairs, on the sequence SEQ ID NO:1.

FIG. 2: Depiction of the aFGF protein which is produced by E. coli BL21, DE3 in the absence of antibiotic and in the presence of the plasmid pXL2283, pXL2434 or pXL2435 following induction with IPTG. The total cell extracts are loaded on the gel. M: molecular weight marker with molecular weights indicated in kDa; the arrow indicates the molecular weight of the aFGF. Sequence SEQ ID NO:1: Nucleotide sequence of the 8501 bp plasmid pXL2435. Position 1 on the sequence corresponds to the BqlII cleavage site of pET11a. The aFGF gene is situated between positions 108 and 575, and the par locus is situated between positions 6038 and 8499, i.e. parE' from 8248 to 8499, parD from 8001 to 8252, parC from 7850 to 7557, parB from 7560 to 7027 and parA from 7066 to 6407; the T7 TΦ promoter is situated between positions 20 and 36, lacO between positions 39 and 63, the T7 TΦ terminator between positions 586 and 708 and the lacI^(q) gene between positions 5636 and 4554.

GENERAL CLONING, MOLECULAR BIOLOGICAL AND BIOCHEMICAL TECHNIQUES

The standard molecular biological methods such as centrifugation of plasmid DNA in a caesium chloride/ethidium bromide gradient, restriction enzyme digestion, gel electrophoresis, electroelution of DNA fragments from agarose gels, transformation into E. coli, nucleic acid precipitation, etc., are described in the literature (Sambrook et al., 1989). The restriction enzymes were supplied by New-England Biolabs (Biolabs), Bethesda Research Laboratories (BRL) or Amersham Ltd (Amersham).

For the ligations, the DNA fragments are separated according to their size on 0.7% agarose gels, purified by electroelution, extracted with phenol, precipitated with ethanol and then incubated in a 50 mM tris-HCl, pH 7.4, 10 mM MgCl2, 10 mM DTT, 2 mM ATP buffer in the presence of phage T4 DNA ligase (Biolabs). The ligated DNAs or pure plasmid DNAs are used to transform the strain: E. coli BL21, DE3 [F⁻ ompT hsdS_(B) (r_(B) ⁻ m_(B) ⁻) qal dcm (DE3)] (Studier et al., 1990) and E. coli TG1 [Δ(lac proA,B), supE, thi, hsdD5/F' traD36, proA⁺, B⁺, lacI^(q), lacZΔM15] (Gibson, 1984) which has been rendered competent. The plasmid DNA samples are purified by the alkaline lysis technique described by Sambrook et al., 1989.

The LB culture medium is used for the bacteriological section (Sambrook et al., 1989). Dilutions of the bacterial suspension are then spread on LB medium plates which are supplemented, if necessary, with 50 mg/l kanamycin.

The protocol described by Studier et al., 1990 is used to produce aFGF with the aid of strain BL21, DE3, which harbours a plasmid for expressing aFGF (pXL2283 or pXL2434 or pXL2435, as described in Example 1).

The production of aFGF is measured on total cell extracts. After the bacteria have been lysed, the samples are loaded onto a 15% SDS-PAGE gel which, after electrophoresis, is stained with Coomassie blue (Denefle et al., 1987). The samples derived from strains which are producing aFGF exhibit a band having an apparent molecular weight of 16 kDa. Semi-dry transfer onto a nitrocellulose membrane is carried out (Sambrook et al., 1989) and the membrane is treated in accordance with the protocol accompanying the Vectastain kit (Biosys SA, France) in order to permit calorimetric immunological (anti-bovine aFGF antibody obtained from rabbit and sold by Sigma, France; and anti-rabbit IgG) detection of the aFGF using the avidin/biotinylated peroxidase complex. Another semidry transfer onto a Pro-Blott membrane is carried out (Matsudaira, 1987), the membrane is stained with Coomassie blue and the band of apparent molecular weight of 16 kDa is excised. This membrane piece is subjected to an Edman, 1956, degradation using a model 477A Applied Biosystems microsequencer which possesses an on-line 120/7 analyser and which is used in accordance with the manufacturer's instructions.

EXAMPLE 1

Construction of a stable and regulated plasmid for expressing the cDNA of human aFGF.

This example describes the constructions which were carried out in order to obtain a stable and highly regulated plasmid for producing aFGF in E. coli.

The cDNA of the native form of the human aFGF gene (470 bp) (Jaye et al., 1986 and 1987) was identified, sequenced and cloned into the expression vector pET9 (Studier et al., 1990) at the NdeI and BamHI sites in order to produce the expression plasmid pMJ42, which is subsequently designated pXL2283 (see FIG. 1). The 2.8 kb NdeI-AccI insert from plasmid pXL2283 was ligated with the 3.2 kb NdeI-AccI fragment from plasmid pET11a (Studier et al., 1990) in order to create the expression plasmid pXL2434. This plasmid differs from pXL2283 in that it also possesses the lacI^(q) gene and the lacO operator, which enable the aFGF to be expressed in a more regulated manner. BamHI sites were then introduced at the ends of the 2.46 kb parCBA-parDE' fragment derived from plasmid pGMA28 (Gerlitz et al., 1990). In order to do this, the 2.46 kb SphI-SphI-BamHI fragment from pGMA28 was cloned into plasmid pUC18 (Yanish-Perron et al., 1985), which was digested with SphI-BamHI, in order to produce plasmid pGMA60 (H. Schwab et al., personal communication). The 2.46 kb HindIII-EcoRI fragment from plasmid pGMA60 was then cloned into plasmid pMTL22 (Chambers et al., 1988), which was digested with HindIII and EcoRI, in order to produce pXL2433. The BamHI (parCBA-parDE') insert from plasmid pXL2433 was introduced into the BalII site of plasmid pXL2434 in order to create plasmid pXL2435. A diagram of the constructions, and the map of plasmid pXL2435, are depicted in FIG. 1, and the 8501 bp sequence of plasmid pXL2435 is described (SEQ ID NO:1). While the sequence described in the paper by Gerlitz et al., 1990 is only partial (125 base pairs are to be added at the 3' end), this 3' part of the sequence was verified on plasmids pXL2433 and pXL2435 and on the sequence SEQ ID NO:1. A summary of the characteristics of the three expression plasmids is presented in Table 1.

                  TABLE 1                                                          ______________________________________                                         Characteristics of the expression plasmids                                                     pXL2283 or                                                                                         Plasmids pMJ42 pXL2434 pXL2435             ______________________________________                                         Size (kb)   4.8         6        8.5                                             Derived from pBR322 pBR322 pBR322                                              Resistance to kanamycin kanamycin kanamycin                                    promoter pT7 T7 Φ10 T7 Φ10 T7 Φ10                                  lacO - + +                                                                     TΦ terminator T7 TΦ T7 TΦ T7 TΦ                                aFGF cDNA + + +                                                                lacI.sup.q - + +                                                               parCBA-ParDE' - - +                                                          ______________________________________                                    

EXAMPLE 2

Stability of the expression plasmid while producing aFGF

This example describes the production, in liquid medium, of aFGF from a recombinant E. coli. strain harbouring a plasmid for the expression of aFGF which is T7 polymerase-dependent and which strain is cultured without selection for the plasmid. Following aFGF production, the presence of the plasmid is monitored by means of the resistance of the bacteria to kanamycin, the resistance gene of which is carried by the plasmids described in Example 1. Finally, the aFGF protein which has been produced is characterized by standard biochemical methods.

EXAMPLE 2.1

Stability of the expression plasmid in the absence of conditions for inducing aFGF production.

Plasmids pXL2283, pXL2434 and pXL2435 are introduced, by transformation, into the BL21, DE3 strain (Studier et al., 1990). Two transformants are taken at random from among the transformants which are selected on LB agar medium containing kanamycin and cultured for 16 hours in liquid LB medium in the presence of kanamycin. The culture is diluted 1/100 and cultured in LB medium in the presence of kanamycin until the optical density at 600 nm is between 0.2 and 0.6. The cultures are diluted 1/100 in 10 ml of LB medium and the strains are cultured up to an OD of between 0.17 and 0.6. This dilution and growth of the bacteria, at 37° C., in medium which does not contain antibiotic is repeated six times and corresponds to a total of more than 30 generations, after a period of two days. The bacteria are spread on LB agar. After they have grown, 100 clones are streaked on LB agar and on LB agar containing Km. Table 2 shows the incidence of clones which are resistant to Km after at least 30 generations without selection pressure for the plasmid.

This example demonstrates that the RP4 par fragment stabilizes the plasmid in the absence of selection pressure, even though this stabilization effect is only moderate.

EXAMPLE 2.2

Stability of the expression plasmid under conditions for inducing aFGF production.

The bacteria which have been cultured for at least 30 generations in the absence of antibiotic (as described in Example 2.1) are diluted 1/100 in LB medium and cultured for 12 hours, and then diluted once again 1/100 in LB medium. When the bacteria have grown to an OD of 0.5 to 0.8, 1 mM IPTG is added and the bacteria are cultured for 4 hours in order to produce aFGF, which is measured on the total cell extracts which are loaded onto a 15% SDS-PAGE gel which is stained with Coomassie blue (see FIG. 2). The bacteria are spread on LB agar. After they have grown, 100 clones are streaked on LB agar and LB agar containing kanamycin. Table 2 shows the incidence of clones which are resistant to kanamycin after having produced aFGF in the absence of selection pressure for the plasmid.

This example demonstrates, unambiguously, that the par fragment induces very substantial segregational stability subsequent to aFGF expression employing the phage T7 polymerase-dependent expression system.

                  TABLE 2                                                          ______________________________________                                         Percentage of clones resistant to kanamycin following                            growth alone, or growth (at least 30 generations) and then                     expression, without any selection pressure for the plasmid                     Culture dilution without                                                                           Culture expression without                                 kanamycin kanamycin                                                                           Percentage      Percentage                                       Number of of clones Number of of clones                                       Plasmid gener- resistant gener- resistant Production                           pXL ations to Km ations to Km of aFGF                                        ______________________________________                                         2283 (No. 1)                                                                           30        20      45     0.1    ε                                2283 (No. 2) 30  10 45 0.2 ε                                           2434 (No. 1) 40 100 45 1 ++                                                    2434 (No. 2) 40  99 45 5 ++                                                    2435 (No. 1) 40 100 45 99 ++                                                   2435 (No. 1) 40 100 45 100 ++                                                ______________________________________                                          ε: expression of aFGF not detected following staining with             Coomassie blue                                                                 ++: very high expression of aFGF; approximately 10% of the total protein.

EXAMPLE 2.3

Characterization of the aFGF protein which is produced in the presence of the plasmid for expressing aFGF.

When produced under the induction conditions described in Example 2.2, the aFGF protein which is obtained is visualized on a 15% PAGE-SDS gel which is stained with Coomassie blue, see FIG. 2, and migrates with an apparent molecular weight of 16 kDa, in accordance with the reported biochemical findings and the published sequence (Jaye et al., 1986 and 1987). Furthermore, this protein is demonstrated by calorimetric immunological detection using anti-bovine aFGF antibodies. The N-terminal sequence of the protein produced by strain BL21, DE3 pXL2435 was then determined using the total extract, which was purified by PAGE-SDS electrophoresis, as described in the general biochemical techniques. The sequence which was obtained is A-E-G-E-I-T-T-F-T-A-L-T (SEQ ID NO: 2); it is identical to the N-terminal sequence of the native protein (Jaye et al., 1986), and the terminal methionine was cleaved off by the E. coli methionylaminopeptidase, as was discussed by Hirel et al., 1989.

This example demonstrates, therefore, that the protein which is produced using an expression plasmid which is stable in E. coli, as described in Example 2.2, is the aFGF protein and that its N-terminal sequence is not truncated.

REFERENCES

Chambers, S., Prior, S., Barstow, D., and Minton, N. (1988) Gene 68: 139-149.

Denefle P., Kovarik, S., Guiton, J. D., Cartwright, T., and Mayaux, J. -F. (1987) Gene 56: 61-70.

Eberl L., Kristensen C., Givskov M., Grohmann E., Gerlitz M., and Schawb H. (1994) Mol. Microbiol. 12: 131-141.

Edman P. (1956) Acta Chemica Scandinavia 10: 761-768.

Gerlitz et al., (1990) J. Bact. 172: 6194-6203

Gibson T. (1984) Ph.D., University of Cambridge, Cambridge, England.

Hirel P., Schmitter P., Dessen P., and Blanquet S. (1989) Proc. Natl. Acad. Sci. 86: 8247-8251.

Jaye M., Howk R., Burgess W., Ricca G., Chui I., Ravera M., O'Brien S., Modi W., Maciag T., and Drohan W. (1986) Science 233: 541-545.

Jaye M., Burgess W., Shaw A., Drohan W. (1987) J. Biol. Chem. 262: 16612-16617.

Matsudaira P. (1987) J. Biol. Chem. 262: 10035-10038.

Roberts et al. (1994) J. Mol. Bol. 237: 35-51.

Sambrook J., Fritsch, E. F., and Maniatis, T. (1989) Molecular Cloning: a Laboratory Manual 2nd edn. Cold Spring Harbor, N.Y.: Cold Spring Harbor Laboratory Press.

Studier, W. F., Rosenberg, A. H., Dunn, J. J., and Duberndorff, J. W. (1990) Methods Enzymol. 185: 89-60.

Yanisch-Perron, C., Vieira, J., Messing, J. (1985) Gene 33: 1033-119.

    __________________________________________________________________________     #             SEQUENCE LISTING                                                    - -  - - (1) GENERAL INFORMATION:                                              - -    (iii) NUMBER OF SEQUENCES: 2                                            - -  - - (2) INFORMATION FOR SEQ ID NO:1:                                      - -      (i) SEQUENCE CHARACTERISTICS:                                                  (A) LENGTH: 8501 base - #pairs                                                 (B) TYPE: nucleic acid                                                         (C) STRANDEDNESS: double                                                       (D) TOPOLOGY: circular                                                - -     (ii) MOLECULE TYPE: cDNA                                               - -     (xi) SEQUENCE DESCRIPTION: SEQ ID NO:1:                                - - GATCTCGATC CCGCGAAATT AATACGACTC ACTATAGGGG AATTGTGAGC GG -             #ATAACAAT     60                                                                  - - TCCCCTCTAG AAATAATTTT GTTTAACTTT AAGAAGGAGA TATACATATG GC -             #TGAAGGGG    120                                                                  - - AAATCACCAC CTTCACAGCC CTGACCGAGA AGTTTAATCT GCCTCCAGGG AA -             #TTACAAGA    180                                                                  - - AGCCCAAACT CCTCTACTGT AGCAACGGGG GCCACTTCCT GAGGATCCTT CC -             #GGATGGCA    240                                                                  - - CAGTGGATGG GACAAGGGAC AGGAGCGACC AGCACATTCA GCTGCAGCTC AG -             #TGCGGAAA    300                                                                  - - GCGTGGGGGA GGTGTATATA AAGAGTACCG AGACTGGCCA GTACTTGGCC AT -             #GGACACCG    360                                                                  - - ACGGGCTTTT ATACGGCTCA CAGACACCAA ATGAGGAATG TTTGTTCCTG GA -             #AAGGCTGG    420                                                                  - - AGGAGAACCA TTACAACACC TATATATCCA AGAAGCATGC AGAGAAGAAT TG -             #GTTTGTTG    480                                                                  - - GCCTCAAGAA GAATGGGAGC TGCAAACGCG GTCCTCGGAC TCACTATGGC CA -             #GAAAGCAA    540                                                                  - - TCTTGTTTCT CCCCCTGCCA GTCTCTTCTG ATTAAAGAGA TCCGGCTGCT AA -             #CAAAGCCC    600                                                                  - - GAAAGGAAGC TGAGTTGGCT GCTGCCACCG CTGAGCAATA ACTAGCATAA CC -             #CCTTGGGG    660                                                                  - - CCTCTAAACG GGTCTTGAGG GGTTTTTTGC TGAAAGGAGG AACTATATCC GG -             #ATATCCAC    720                                                                  - - AGGACGGGTG TGGTCGCCAT GATCGCGTAG TCGATAGTGG CTCCAAGTAG CG -             #AAGCGAGC    780                                                                  - - AGGACTGGGC GGCGGCCAAA GCGGTCGGAC AGTGCTCCGA GAACGGGTGC GC -             #ATAGAAAT    840                                                                  - - TGCATCAACG CATATAGCGC TAGCAGCACG CCATAGTGAC TGGCGATGCT GT -             #CGGAATGG    900                                                                  - - ACGATATCCC GCAAGAGGCC CGGCAGTACC GGCATAACCA AGCCTATGCC TA -             #CAGCATCC    960                                                                  - - AGGGTGACGG TGCCGAGGAT GACGATGAGC GCATTGTTAG ATTTCATACA CG -             #GTGCCTGA   1020                                                                  - - CTGCGTTAGC AATTTAACTG TGATAAACTA CCGCATTAAA GCTTATCGAT GA -             #TAAGCTGT   1080                                                                  - - CAAACATGAG AATTCTTAGA AAAACTCATC GAGCATCAAA TGAAACTGCA AT -             #TTATTCAT   1140                                                                  - - ATCAGGATTA TCAATACCAT ATTTTTGAAA AAGCCGTTTC TGTAATGAAG GA -             #GAAAACTC   1200                                                                  - - ACCGAGGCAG TTCCATAGGA TGGCAAGATC CTGGTATCGG TCTGCGATTC CG -             #ACTCGTCC   1260                                                                  - - AACATCAATA CAACCTATTA ATTTCCCCTC GTCAAAAATA AGGTTATCAA GT -             #GAGAAATC   1320                                                                  - - ACCATGAGTG ACGACTGAAT CCGGTGAGAA TGGCAAAAGC TTATGCATTT CT -             #TTCCAGAC   1380                                                                  - - TTGTTCAACA GGCCAGCCAT TACGCTCGTC ATCAAAATCA CTCGCATCAA CC -             #AAACCGTT   1440                                                                  - - ATTCATTCGT GATTGCGCCT GAGCGAGACG AAATACGCGA TCGCTGTTAA AA -             #GGACAATT   1500                                                                  - - ACAAACAGGA ATCGAATGCA ACCGGCGCAG GAACACTGCC AGCGCATCAA CA -             #ATATTTTC   1560                                                                  - - ACCTGAATCA GGATATTCTT CTAATACCTG GAATGCTGTT TTCCCGGGGA TC -             #GCAGTGGT   1620                                                                  - - GAGTAACCAT GCATCATCAG GAGTACGGAT AAAATGCTTG ATGGTCGGAA GA -             #GGCATAAA   1680                                                                  - - TTCCGTCAGC CAGTTTAGTC TGACCATCTC ATCTGTAACA TCATTGGCAA CG -             #CTACCTTT   1740                                                                  - - GCCATGTTTC AGAAACAACT CTGGCGCATC GGGCTTCCCA TACAATCGAT AG -             #ATTGTCGC   1800                                                                  - - ACCTGATTGC CCGACATTAT CGCGAGCCCA TTTATACCCA TATAAATCAG CA -             #TCCATGTT   1860                                                                  - - GGAATTTAAT CGCGGCCTCG AGCAAGACGT TTCCCGTTGA ATATGGCTCA TA -             #ACACCCCT   1920                                                                  - - TGTATTACTG TTTATGTAAG CAGACAGTTT TATTGTTCAT GACCAAAATC CC -             #TTAACGTG   1980                                                                  - - AGTTTTCGTT CCACTGAGCG TCAGACCCCG TAGAAAAGAT CAAAGGATCT TC -             #TTGAGATC   2040                                                                  - - CTTTTTTTCT GCGCGTAATC TGCTGCTTGC AAACAAAAAA ACCACCGCTA CC -             #AGCGGTGG   2100                                                                  - - TTTGTTTGCC GGATCAAGAG CTACCAACTC TTTTTCCGAA GGTAACTGGC TT -             #CAGCAGAG   2160                                                                  - - CGCAGATACC AAATACTGTC CTTCTAGTGT AGCCGTAGTT AGGCCACCAC TT -             #CAAGAACT   2220                                                                  - - CTGTAGCACC GCCTACATAC CTCGCTCTGC TAATCCTGTT ACCAGTGGCT GC -             #TGCCAGTG   2280                                                                  - - GCGATAAGTC GTGTCTTACC GGGTTGGACT CAAGACGATA GTTACCGGAT AA -             #GGCGCAGC   2340                                                                  - - GGTCGGGCTG AACGGGGGGT TCGTGCACAC AGCCCAGCTT GGAGCGAACG AC -             #CTACACCG   2400                                                                  - - AACTGAGATA CCTACAGCGT GAGCTATGAG AAAGCGCCAC GCTTCCCGAA GG -             #GAGAAAGG   2460                                                                  - - CGGACAGGTA TCCGGTAAGC GGCAGGGTCG GAACAGGAGA GCGCACGAGG GA -             #GCTTCCAG   2520                                                                  - - GGGGAAACGC CTGGTATCTT TATAGTCCTG TCGGGTTTCG CCACCTCTGA CT -             #TGAGCGTC   2580                                                                  - - GATTTTTGTG ATGCTCGTCA GGGGGGCGGA GCCTATGGAA AAACGCCAGC AA -             #CGCGGCCT   2640                                                                  - - TTTTACGGTT CCTGGCCTTT TGCTGGCCTT TTGCTCACAT GTTCTTTCCT GC -             #GTTATCCC   2700                                                                  - - CTGATTCTGT GGATAACCGT ATTACCGCCT TTGAGTGAGC TGATACCGCT CG -             #CCGCAGCC   2760                                                                  - - GAACGACCGA GCGCAGCGAG TCAGTGAGCG AGGAAGCGGA AGAGCGCCTG AT -             #GCGGTATT   2820                                                                  - - TTCTCCTTAC GCATCTGTGC GGTATTTCAC ACCGCATATA TGGTGCACTC TC -             #AGTACAAT   2880                                                                  - - CTGCTCTGAT GCCGCATAGT TAAGCCAGTA TACACTCCGC TATCGCTACG TG -             #ACTGGGTC   2940                                                                  - - ATGGCTGCGC CCCGACACCC GCCAACACCC GCTGACGCGC CCTGACGGGC TT -             #GTCTGCTC   3000                                                                  - - CCGGCATCCG CTTACAGACA AGCTGTGACC GTCTCCGGGA GCTGCATGTG TC -             #AGAGGTTT   3060                                                                  - - TCACCGTCAT CACCGAAACG CGCGAGGCAG CTGCGGTAAA GCTCATCAGC GT -             #GGTCGTGA   3120                                                                  - - AGCGATTCAC AGATGTCTGC CTGTTCATCC GCGTCCAGCT CGTTGAGTTT CT -             #CCAGAAGC   3180                                                                  - - GTTAATGTCT GGCTTCTGAT AAAGCGGGCC ATGTTAAGGG CGGTTTTTTC CT -             #GTTTGGTC   3240                                                                  - - ACTGATGCCT CCGTGTAAGG GGGATTTCTG TTCATGGGGG TAATGATACC GA -             #TGAAACGA   3300                                                                  - - GAGAGGATGC TCACGATACG GGTTACTGAT GATGAACATG CCCGGTTACT GG -             #AACGTTGT   3360                                                                  - - GAGGGTAAAC AACTGGCGGT ATGGATGCGG CGGGACCAGA GAAAAATCAC TC -             #AGGGTCAA   3420                                                                  - - TGCCAGCGCT TCGTTAATAC AGATGTAGGT GTTCCACAGG GTAGCCAGCA GC -             #ATCCTGCG   3480                                                                  - - ATGCAGATCC GGAACATAAT GGTGCAGGGC GCTGACTTCC GCGTTTCCAG AC -             #TTTACGAA   3540                                                                  - - ACACGGAAAC CGAAGACCAT TCATGTTGTT GCTCAGGTCG CAGACGTTTT GC -             #AGCAGCAG   3600                                                                  - - TCGCTTCACG TTCGCTCGCG TATCGGTGAT TCATTCTGCT AACCAGTAAG GC -             #AACCCCGC   3660                                                                  - - CAGCCTAGCC GGGTCCTCAA CGACAGGAGC ACGATCATGC GCACCCGTGG CC -             #AGGACCCA   3720                                                                  - - ACGCTGCCCG AGATGCGCCG CGTGCGGCTG CTGGAGATGG CGGACGCGAT GG -             #ATATGTTC   3780                                                                  - - TGCCAAGGGT TGGTTTGCGC ATTCACAGTT CTCCGCAAGA ATTGATTGGC TC -             #CAATTCTT   3840                                                                  - - GGAGTGGTGA ATCCGTTAGC GAGGTGCCGC CGGCTTCCAT TCAGGTCGAG GT -             #GGCCCGGC   3900                                                                  - - TCCATGCACC GCGACGCAAC GCGGGGAGGC AGACAAGGTA TAGGGCGGCG CC -             #TACAATCC   3960                                                                  - - ATGCCAACCC GTTCCATGTG CTCGCCGAGG CGGCATAAAT CGCCGTGACG AT -             #CAGCGGTC   4020                                                                  - - CAGTGATCGA AGTTAGGCTG GTAAGAGCCG CGAGCGATCC TTGAAGCTGT CC -             #CTGATGGT   4080                                                                  - - CGTCATCTAC CTGCCTGGAC AGCATGGCCT GCAACGCGGG CATCCCGATG CC -             #GCCGGAAG   4140                                                                  - - CGAGAAGAAT CATAATGGGG AAGGCCATCC AGCCTCGCGT CGCGAACGCC AG -             #CAAGACGT   4200                                                                  - - AGCCCAGCGC GTCGGCCGCC ATGCCGGCGA TAATGGCCTG CTTCTCGCCG AA -             #ACGTTTGG   4260                                                                  - - TGGCGGGACC AGTGACGAAG GCTTGAGCGA GGGCGTGCAA GATTCCGAAT AC -             #CGCAAGCG   4320                                                                  - - ACAGGCCGAT CATCGTCGCG CTCCAGCGAA AGCGGTCCTC GCCGAAAATG AC -             #CCAGAGCG   4380                                                                  - - CTGCCGGCAC CTGTCCTACG AGTTGCATGA TAAAGAAGAC AGTCATAAGT GC -             #GGCGACGA   4440                                                                  - - TAGTCATGCC CCGCGCCCAC CGGAAGGAGC TGACTGGGTT GAAGGCTCTC AA -             #GGGCATCG   4500                                                                  - - GTCGAGATCC CGGTGCCTAA TGAGTGAGCT AACTTACATT AATTGCGTTG CG -             #CTCACTGC   4560                                                                  - - CCGCTTTCCA GTCGGGAAAC CTGTCGTGCC AGCTGCATTA ATGAATCGGC CA -             #ACGCGCGG   4620                                                                  - - GGAGAGGCGG TTTGCGTATT GGGCGCCAGG GTGGTTTTTC TTTTCACCAG TG -             #AGACGGGC   4680                                                                  - - AACAGCTGAT TGCCCTTCAC CGCCTGGCCC TGAGAGAGTT GCAGCAAGCG GT -             #CCACGCTG   4740                                                                  - - GTTTGCCCCA GCAGGCGAAA ATCCTGTTTG ATGGTGGTTA ACGGCGGGAT AT -             #AACATGAG   4800                                                                  - - CTGTCTTCGG TATCGTCGTA TCCCACTACC GAGATATCCG CACCAACGCG CA -             #GCCCGGAC   4860                                                                  - - TCGGTAATGG CGCGCATTGC GCCCAGCGCC ATCTGATCGT TGGCAACCAG CA -             #TCGCAGTG   4920                                                                  - - GGAACGATGC CCTCATTCAG CATTTGCATG GTTTGTTGAA AACCGGACAT GG -             #CACTCCAG   4980                                                                  - - TCGCCTTCCC GTTCCGCTAT CGGCTGAATT TGATTGCGAG TGAGATATTT AT -             #GCCAGCCA   5040                                                                  - - GCCAGACGCA GACGCGCCGA GACAGAACTT AATGGGCCCG CTAACAGCGC GA -             #TTTGCTGG   5100                                                                  - - TGACCCAATG CGACCAGATG CTCCACGCCC AGTCGCGTAC CGTCTTCATG GG -             #AGAAAATA   5160                                                                  - - ATACTGTTGA TGGGTGTCTG GTCAGAGACA TCAAGAAATA ACGCCGGAAC AT -             #TAGTGCAG   5220                                                                  - - GCAGCTTCCA CAGCAATGGC ATCCTGGTCA TCCAGCGGAT AGTTAATGAT CA -             #GCCCACTG   5280                                                                  - - ACGCGTTGCG CGAGAAGATT GTGCACCGCC GCTTTACAGG CTTCGACGCC GC -             #TTCGTTCT   5340                                                                  - - ACCATCGACA CCACCACGCT GGCACCCAGT TGATCGGCGC GAGATTTAAT CG -             #CCGCGACA   5400                                                                  - - ATTTGCGACG GCGCGTGCAG GGCCAGACTG GAGGTGGCAA CGCCAATCAG CA -             #ACGACTGT   5460                                                                  - - TTGCCCGCCA GTTGTTGTGC CACGCGGTTG GGAATGTAAT TCAGCTCCGC CA -             #TCGCCGCT   5520                                                                  - - TCCACTTTTT CCCGCGTTTT CGCAGAAACG TGGCTGGCCT GGTTCACCAC GC -             #GGGAAACG   5580                                                                  - - GTCTGATAAG AGACACCGGC ATACTCTGCG ACATCGTATA ACGTTACTGG TT -             #TCACATTC   5640                                                                  - - ACCACCCTGA ATTGACTCTC TTCCGGGCGC TATCATGCCA TACCGCGAAA GG -             #TTTTGCGC   5700                                                                  - - CATTCGATGG TGTCCGGGAT CTCGACGCTC TCCCTTATGC GACTCCTGCA TT -             #AGGAAGCA   5760                                                                  - - GCCCAGTAGT AGGTTGAGGC CGTTGAGCAC CGCCGCCGCA AGGAATGGTG CA -             #TGCAAGGA   5820                                                                  - - GATGGCGCCC AACAGTCCCC CGGCCACGGG GCCTGCCACC ATACCCACGC CG -             #AAACAAGC   5880                                                                  - - GCTCATGAGC CCGAAGTGGC GAGCCCGATC TTCCCCATCG GTGATGTCGG CG -             #ATATAGGC   5940                                                                  - - GCCAGCAACC GCACCTGTGG CGCCGGTGAT GCCGGCCACG ATGCGTCCGG CG -             #TAGAGGAT   6000                                                                  - - CGAGATCCAT ATGACGTCGA CGCGTCTGCA GAAGCTTGCA TGCCAGCTTC TG -             #GTTCGTCG   6060                                                                  - - GCTGGGTGAT GGCGTCGGTT TTGGCCGGCG GCGTCGGCGC GATCGCCAGC GC -             #GAAGCAAC   6120                                                                  - - TGGCGTTCCT CGGCGAACAT AGCGGCATGG TGGCCTTCGG CTTCTTCCGC GA -             #CCAGGTGA   6180                                                                  - - AGGACATGCA CTGCGATGCG GACGTGATCC TGGCCCGGTG GGATGAAAAG GC -             #GAACTCGC   6240                                                                  - - CGGTGGTCTA CCGCTGCCCG AAGGCGTACC TGCTCAACAG GTTCGCATCC GC -             #GCCCTTCG   6300                                                                  - - TGCCCTGGCC GGACTACACC GAGGGGGAAA GCGAGGATCT AGGTAGGGCG CT -             #CGCAGCGG   6360                                                                  - - CCCTGCGGGA CGCGAAAAGG TGAGAAAAGC CGGGCACTGC CCGGCTTTAT TT -             #TTGCTGCT   6420                                                                  - - GCGCGTTCCA GGCCGCCCAC ACTCGTTTGA CCTGGCTCGG GCTGCATCCG AC -             #CAGCTTGG   6480                                                                  - - CCGTCTTGGC AATGCTCGAT CCGCCGGAGC GAAGCGTGAT GATGCGGTCG TG -             #CATGCCGG   6540                                                                  - - CGTCACGTTT GCGGCCGGTG TAGCGGCCGG CGGCCTTCGC CAACTGGACA CC -             #CTGACGTT   6600                                                                  - - GACGCTCGCG CCGATCCTCG TAGTCGTCGC GGGCCATCTG CAAGGCGAGC TT -             #CAAAAGCA   6660                                                                  - - TGTCCTGGAC GGATTCCAGA ACGATTTTCG CCACTCCGTT CGCCTCGGCG GC -             #CAGCTCCG   6720                                                                  - - ACAGGTCCAC CACGCCAGGC ACGGCCAGCT TGGCCCCTTT GGCCCGGATC GA -             #CGCAACCA   6780                                                                  - - GGCGCTCGGC CTCGGCCAAC GGCAAGCGGC TGATGCGGTC GATCTTCTCC GC -             #AACGACGA   6840                                                                  - - CTTCACCAGG TTGCAGGTCC GCGATCATGC GCAGCAGCTC GGGCCGGTCG GC -             #GCGTGCGC   6900                                                                  - - CGGACGCCTT CTCGCGGTAG ATGCCGGCGA CGTAGTACCC GGCGGCCCGC GT -             #GGCCGCTA   6960                                                                  - - CAAGGCTCTC CTGGCGTTCA AGATTCTGCT CGTCCGTACT GGCGCGCAGG TA -             #GATGCGGG   7020                                                                  - - CGACCTTCAA CCTTCGTCCC TCCGGTTGTT GCTCTCGCGT CGCCATTTCC AC -             #GGCTCGAC   7080                                                                  - - GGCGTGCGGA TCGGACCAGA GGCCGACGCG CTTGCCTCGC GCCTCCTGTT CG -             #AGCCGCAG   7140                                                                  - - CATTTCAGGG TCGGCCGCGC GGCCGTGGAA GCGATAGGCC CACGCCATGC CC -             #TGGTGAAC   7200                                                                  - - CATCGCGGCG TTGACGTTGC GCGGCTGCGG CGGCCGGCTG GCCAGCTCCA TG -             #TTGACCCA   7260                                                                  - - CACGGTGCCC AGCGTGCGGC CGTAACGGTC GGTGTCCTTC TCGTCGACCA GG -             #ACGTGCCG   7320                                                                  - - GCGGAACACC ATGCCGGCCA GCGCCTGGCG CGCACGTTCG CCGAAGGCTT GC -             #CGCTTTTC   7380                                                                  - - CGGCGCGTCA ATGTCCACCA GGCGCACGCG CACCGGCTGC TTGTCTACCA GC -             #ACGTCGAT   7440                                                                  - - GGTGTCGCCG TCGATGATGC GCACGACCTC GCCGCGCAGC TCGGCCCATG CC -             #GGCGAGGC   7500                                                                  - - AACGACCAGG ACGGCCAGCG CGGCAGCGGC GCGCAGCATG GCGTAGCTTC GG -             #CGCTTCAT   7560                                                                  - - GCGTGGCCCC ATTGCTGATG ATCGGGGTAC GCCAGGTGCA GCACTGCATC GA -             #AATTGGCC   7620                                                                  - - TTGCAGTAGC CGTCCAGCGC CACCCGCGAG CCGAACGCCG GCGAAAGGTA CT -             #CGACCAGG   7680                                                                  - - CCGGGCCGGT CGCGGACCTC GCGCCCCAGG ACGTGGATGC GCCGGCCGCG TG -             #TGCCGTCG   7740                                                                  - - GGTCCAGGCA CGAAGGCCAG CGCCTCGATG TTGAAGTCGA TGGATAGAAG TT -             #GTCGGTAG   7800                                                                  - - TGCTTGGCCG CCCTCATCGC GTCCCCCTTG GTCAAATTGG GTATACCCAT TT -             #GGGCCTAG   7860                                                                  - - TCTAGCCGGC ATGGCGCATT ACAGCAATAC GCAATTTAAA TGCGCCTAGC GC -             #ATTTTCCC   7920                                                                  - - GACCTTAATG CGCCTCGCGC TGTAGCCTCA CGCCCACATA TGTGCTAATG TG -             #GTTACGTG   7980                                                                  - - TATTTTATGG AGGTTATCCA ATGAGCCGCC TGACAATCGA CATGACGGAC CA -             #GCAGCACC   8040                                                                  - - AGAGCCTGAA AGCCCTGGCC GCCTTGCAGG GCAAGACCAT TAAGCAATAC GC -             #CCTCGAAC   8100                                                                  - - GTCTGTTCCC CGGTGACGCT GATGCCGATC AGGCATGGCA GGAACTGAAA AC -             #CATGCTGG   8160                                                                  - - GGAACCGCAT CAACGATGGG CTTGCCGGCA AGGTGTCCAC CAAGAGCGTC GG -             #CGAAATTC   8220                                                                  - - TTGATGAAGA ACTCAGCGGG GATCGCGCTT GACGGCCTAC ATCCTCACGG CT -             #GAGGCCGA   8280                                                                  - - AGCCGATCTA CGCGGCATCA TCCGCTACAC GCGCCGGGAG TGGGGCGCGG CG -             #CAGGTGCG   8340                                                                  - - CCGCTATATC GCTAAGCTGG AACAGGGCAT AGCCAGGCTT GCCGCCGGCG AA -             #GGCCCGTT   8400                                                                  - - TAAGGACATG AGCGAACTCT TTCCCGCGCT GCGGATGGCC CGCTGCGAAC AC -             #CACTACGT   8460                                                                  - - TTTTTGCCTG CCGCGTGCGG GCGAACCCGC GTTGGTCGTC G    - #                       - # 8501                                                                      - -  - - (2) INFORMATION FOR SEQ ID NO:2:                                      - -      (i) SEQUENCE CHARACTERISTICS:                                                  (A) LENGTH: 12 amino - #acids                                                  (B) TYPE: amino acid                                                           (C) STRANDEDNESS:                                                              (D) TOPOLOGY: linear                                                  - -     (ii) MOLECULE TYPE: protein                                            - -     (xi) SEQUENCE DESCRIPTION: SEQ ID NO:2:                                - - Ala Glu Gly Glu Ile Thr Thr Phe Thr Ala Le - #u Thr                       1               5   - #                10                                     __________________________________________________________________________ 

What is claimed is:
 1. An expression plasmid comprising a nucleic acid sequence encoding a protein of interest under the control of a bacteriophage T7 promoter and a stabilizing region comprising all or part of the par region of the plasmid RP4, or of a derivative of the par region wherein said all or part or derivative of the par region of the plasmid RP4 stabilizes the plasmid such that the plasmid may be maintained in bacterial cells without any selection pressure.
 2. A plasmid according to claim 1, wherein the bacteriophage T7 promoter is the promoter of gene
 10. 3. A plasmid according to claim 1, wherein the stabilizing region comprises part of the par region of plasmid RP4.
 4. A plasmid according to claim 3, wherein the stabilizing region comprises residues 6038 to 8499 of the sequence SEQ ID NO:1.
 5. A plasmid according to claim 1, further comprising the lacO operator and the lacI^(q) gene.
 6. A plasmid according to claim 5, wherein the lacO operator is downstream of the bacteriophage T7 promoter and upstream of said nucleic acid.
 7. A plasmid according to claim 1, wherein the protein is of pharmaceutical interest, agrifood interest, or to be used in biocatalysis.
 8. A plasmid according to claim 7, wherein the protein is selected from the group consisting of enzymes, blood products, hormones, lymphokines, growth factors, neurotransmitter synthesizing enzymes, trophic factors, apolipoproteins, dystrophin, minidystrophin, CFTR protein, tumour suppressors, factors involved in coagulation, or proteins involved in DNA repair.
 9. A plasmid according to claim 8, wherein the protein is an acidic fibroblast growth factor (aFGF).
 10. A plasmid according to claim 9, wherein the protein encodes aFGF (154).
 11. A plasmid pXL2435 comprising SEQ ID NO:1.
 12. A process for producing recombinant proteins, said process comprising culturing a bacterium comprising:a plasmid according to claim 1, and a gene encoding the bacteriophage T7 RNA polymerase,under conditions which allow expression of the nucleic acid sequence.
 13. A process according to claim 12, wherein the gene encoding the bacteriophage T7 RNA polymerase is under the control of an inducible promoter.
 14. A process according to claims 12, wherein the gene encoding the bacteriophage T7 RNA polymerase is integrated into the genome of the bacterium.
 15. A process according to claim 12, wherein the bacterium is an E. coli strain.
 16. A process according to claim 15, wherein the bacterium is the E. coli strain BL21, DE3.
 17. A process according to claim 12, wherein said protein is aFGF.
 18. A process for preparing recombinant aFGF, said process comprising culturing a bacterium comprising plasmid pXL2435 and a gene encoding the bacteriophage T7 RNA polymerase under conditions which produce said aFGF.
 19. A bacterium transformed with a plasmid according to claim
 1. 